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oral presentation; International audience; This work concerns the propagation of elastic waves in a piezoelectric phononic crystal made of several identical piezoelectric elements separated by electrodes. In such a structure, electrical conditions prescribed to the electrodes can be modulated in space and in time and therefore can strongly modify the dispersion curves of the phononic crystal. For example, a periodic grounding of the electrodes introduces a Bragg band gap which does not exist when the electrodes have a floating potential condition [Degraeve et al., J. Appl. Phys. 115, (2014)]. When the electrical conditions of the electrodes are modulated in space and in time, dispersion curves are tilted with respect to the configuration in the reference medium and nonreciprocal wave propagation may occur at some modulation speeds in specific frequency bands [Croënne et al., Appl. Phys. Lett. 110 , (2017)]. The experimental set-up is based on a stack of 113 piezoelectric rings and 114 electrodes. The spatio-temporal modulation of the electrical conditions is performed using a digital signal processor (DSP) in order to reach high modulation speeds. This modulation is performed by shifting the position of the periodic ground conditions of the electrodes versus time. The experimental dispersion curves are obtained using measurements of the normal displacement of the piezoelectric rings with a scanning laser vibrometer. The evolution of dispersion curves as a function of modulation speed is analyzed and compared to finite element simulation results.

The unidirectional flow of electrons that takes place in a conventional electronic diode has been a cornerstone in the development of the field of electronics. Achieving an equivalent one-way flow for light has been a long-standing problem. While a number of concepts have been suggested recently, attaining a unidirectional flow of light in a two-port system (e.g., a waveguiding configuration) is still challenging. Here, we present what we believe to be a novel approach for breaking reciprocity and achieving one-way flow of light. Taking a nanoplasmonic waveguide as an example, we show that a combination of time-dependent interband optical transitions, when in systems exhibiting a backward wave flow, can yield light transmission strictly in one direction. In our configuration, the energy flow is unidirectional: light is fully reflected in one direction of propagation, and is unperturbed in the other. The concept can find use in a range of applications including communications, smart windows, thermal radiation management, and solar energy harvesting.

SummaryAt the basis of cell shape and behavior, actomyosin organization and force-generating property are widely studied, however very little is known about the regulation of the contractile network in space and time. Here we study the role of the epithelial-specific protein EpCAM, a contractility modulator, in cell shape and motility, and we show that it is required for the maturation of stress fibers and frontrear polarity acquisition at the single cell level. There, EpCAM ensures the remodeling of a transient active RhoA zone in the cortex of spreading epithelial cells. GTP-RhoA follows the endosomal pathway mediated by Rab35 and EHD1, where it co-evolves together with EpCAM. In fact, EpCAM balances GTP-RhoA turnover in order to tune actomyosin remodeling for cell shape, polarity and mechanical property acquisition. Impairment of GTP-RhoA endosomal trafficking either by EpCAM silencing or Rab35 / EHD1 mutant expression prevents correct myosin-II activity, stress fiber formation, and ultimately cell polarization. Collectively, this work shows that the coupling of EpCAM/RhoA co-trafficking to actomyosin rearrangement is critical for spreading, and advances our understanding of how biochemical and mechanical properties can be coupled for cell plasticity.

Conventional microwave circulators rely on ferro-magentic materials to break the time-reversal symmetry, and thus realizing a non-reciprocal passive device. In terms of system design, the use of ferromagentic materials renders the circulator integration with other transceiver blocks difficult, because they are still incompatible with CMOS fabrication processes. Recently, the concept of spatio-temporal modulation has been introduced to break the time-reversal symmetry, alleviating the need of ferromagnetic materials. In this paper, we present the design of a magnetic-less linear passive circulator based on spatio-temporal modulation of lumped first order LC resonators connected in a Y topology. Unlike other approaches, in this work the spatiotemporal modulation is implemented using switched capacitors, which yield a much simple circuit and has the advantage of high linearity. As a proof of concept, we designed a circulator at 1 GHz that shows an isolation of 44 dB with an insertion loss of 2.9 dB.

Spatio-temporal modulation (STM) has been recently introduced to efficiently implement angular momentum biasing, which is a biasing technique that breaks the time reversal symmetry yielding a non-reciprocal response. In literature, several circulators have been designed using STM of triple first-order series or shunt resonators connected in Y or $\Delta$ topology. Utilizing first-order resonators leads to a narrow band response in terms of isolation and return loss. In this paper, we tackle this problem by using a 2-pole series bandpass resonators. As a proof-of-concept, the circulator is designed at 500MHz, and demonstrates a 15-dB isolation fractional bandwidth of 8.5%, insertion loss of 3.9 dB, and return loss of better than 13 dB.)

Most surgeries are currently performed subjectively, with outcomes that are largely dependent on the experience of the surgeon. Providing objective information about tissue that need to be resected or avoided could reduce the variability in surgical outcomes. Spatial Frequency Domain Imaging (SFDI) is a novel diffuse optical imaging method that has the potential to identify tissue viability over a large field of view. In this method, a spatial sinusoidal pattern is projected onto the tissue to get the optical properties of the tissue at each pixel. More recently, Single Snapshot of Optical Properties (SSOP) hase been developed to provide such image feedback in real-time within the specific constraints of surgery. However, while SSOP has been shown to provide information about tissues at a single wavelength in real-time, during surgical applications, it is critical to obtain spectrally-resolved functional information that can be easily interpreted by the surgeons. Optical properties at multiple wavelengths are therefore needed to correlate the absorption and scattering coefficients with the tissue functional and structural information. In this work, we propose a novel method relying on spatio-temporal modulation of light to obtain multispectral optical properties in real time. A temporal-encoding method is used to distinguish different wavelengths by modulating each wavelength at a one particular chosen frequency. The temporally-modulated light is then used to project sinusoidal patterns onto the tissues for SSOP processing. The scene is then recorded with a fast camera to get multiple information in 3 dimensions: two spatial dimensions for SSOP and the third temporal dimension for wavelength. Discrete Fourier Transform (DFT) is used to separate the modulation frequencies pixels by pixels, and each 2D image obtained for every wavelength is processed using SSOP to obtain absorption and scattering coefficients. Finally, the optical properties at each wavelength are used to provide functional and structural information about tissues. We validated this proof of concept using 2 wavelengths (665 and 860nm) during phantom measurements and in vivo by obtaining real-time oxygenation videos. This work lays the foundation for the clinical translation of real-time quantitative multispectral imaging.

Modulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatio-temporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerr-nonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.

The spectacular facets of light have made light ubiquitous in all fields of science. Light’s interaction with matter allows for accurate manipulation of atomic and molecular structures that enabled fundamental breakthroughs in physics, chemistry, and biomedical research. The transfer of light’s energy on molecules and genetically expressed proteins can be used to stimulate cells and emulate cellular processes such as synaptic inputs spatially distributed along the neuron’s dendritic tree. Here, we show basic neuronal functions derived via numerical modelling and describe how we can use light to emulate these functions in order to provide a systematic study of the neuron’s response. We focus on cortical pyramidal neurons and use the NEURON simulation environment to analyze how spatio-temporal stimulation patterns along various dendritic locations sets the neuron to fire an output. We then show an equivalent response from experiments via complex spatial light patterns for stimulating across different regions along the dendritic tree. Furthermore, we use the same spatial light patterns to simultaneously visualize neuronal responses via functional calcium imaging predicted via the same neuron model. Visualizing dendritic responses from back-propagating action potentials can provide new insights to some important features of dendritic computation.

This manuscript details the possibility of achieving one-way sound propagation using a smart fluid such as magnetorheological fluid (MRF) by subjecting it to a spatio-temporally varying magnetic field. The local speed of sound in MRF is dependent on applied magnetic field as demonstrated in several experimental works and this property of MRF has been leveraged, in this work, to induce one-way bandgaps. Initially, a general wave equation pertaining to fluid with space-and-time-varying material properties was derived. Assuming plane wave propagation in one dimension, an approximate Floquet solution was imposed and the dispersion relationship was obtained. A comprehensive finite element analysis was conducted and good agreement was noted between the numerical and theoretical dispersion relations. It was concluded that space-time periodic modulation of fluid density and local sound speed is necessary to induce asymmetry in the band diagram around the ω axis. The feasibility of real-world implementation using MRF has been discussed. A parametric study detailing the effect of viscosity on the one-way bandgaps has been undertaken. It was found that one-way bandgaps formed at relatively lower frequencies are more robust to viscous corruption. A real-world implementation may be feasible if the viscosity of MRF is less than 3000 Pa-s.

A non-reciprocal device using a space-time modulation scheme. By applying the space-time modulation scheme, reciprocity in radiation and scattering scenarios is prevented. Such a scheme utilizes a linear system with simple, compact and inexpensive electronic components compared to the current use of bulky duplexers and non-reciprocal magnet based phase shifters to provide non-reciprocity. One such linear system involves traveling-wave antennas loaded with voltage dependent capacitors that are modulated in space and time thereby allowing the antenna to transmit with high directivity in a certain direction and not receive from that direction. Another linear system involves a resonant metasurface characterized by transverse spatiotemporal gradients, where the spatiotemporal gradients include periodically modulated impedances thereby causing a non-reciprocal transmission response. In this manner, a signal that propagates and impinges on the surface at a given direction will be fully transmitted while a signal propagating from the complementary direction will be fully reflected.

Summary Drought is a major abiotic stress that affects the development and growth of most plants, and limits crop yield worldwide. Although the response of plants to drought has been well documented, much less is known about how plants respond to the water recovery process, namely rehydration. Here, we describe the spatio-temporal response of plant reproductive organs to rehydration using rose flowers as an experimental system. We found that rehydration triggered rapid and transient ethylene production in the gynoecia. This ethylene burst serves as a signal to ensure water recovery in flowers, and promotes flower opening by influencing the expression of a set of rehydration-responsive genes. An in-gel kinase assay suggested that the rehydration-induced ethylene burst resulted from transient accumulation of RhACS1/2 proteins in gynoecia. Meanwhile, RhMPK6, a rose homolog of Arabidopsis thaliana MPK6, is rapidly activated by rehydration within 0.5 h. Furthermore, RhMPK6 was able to phosphorylate RhACS1 but not RhACS2 in vitro. Application of the kinase inhibitor K252a suppressed RhACS1 accumulation and rehydration-induced ethylene production in gynoecia, and the protein phosphatase inhibitor okadaic acid had the opposite effect, confirming that accumulation of RhACS1 was phosphorylation-dependent. Finally, silencing of RhMPK6 significantly reduced ethylene production in gynoecia when flowers were subjected to rehydration. Taken together, our results suggest that temporal- and spatial-specific activation of an RhMPK6-RhACS1 cascade is responsible for rehydration-induced ethylene production in gynoecia, and that the resulting ethylene-mediated signaling pathway is a key factor in flower rehydration.

International audience; The properties of a one-dimensional phononic crystal made of identical piezoelectric elements separated by thin metallic electrodes connected to the ground are studied theoretically for cases where the locations of the electrical connections change as a function of time with a specific speed. This spatio-temporal modulation of the electrical boundary conditions results in significant non-linear effects that are evidenced numerically. The interaction between an incident harmonic longitudinal wave and the time-dependent phononic crystal is shown to lead to frequency splitting analogous to Brillouin scattering. Moreover, the boundaries of the Bragg bandgaps are strongly affected, and for some specific modulation speed, one-way wave propagation can be achieved.

Imaging polarimeters have been largely used for remote sensing tasks, and most imaging polarimeters are division of time or division of space Stokes polarimeters. Imaging Mueller matrix polarimeters have just begun to be constructed which can take data quickly enough to be useful. We have constructed a Mueller matrix (active) polarimeter utilizing a hybrid modulation approach (modulated in both time and space) based on a micropo- larizer array camera and rotating retarders. The hybrid approach allows for an increase in temporal bandwidth (instrument speed) at the expense of spatial bandwidth (sensor resolution). We present the hybrid approach and associated reconstruction schemes here. Additionally, we introduce the instrument design and some preliminary results and data from the instrument.